The main goal is to get to level 50 in every trading company (3) to unlock 'Pirate Legend' which is basically the end goal (For now) which grants you extra quests, a hidden hideout, later update will give you proper Captain capabilities (I.E you own your own ship) and other's will know you're a pirate legend from your ship/clothing.

From what I'm hearing though it definitely needs a tutorial to give people the basics of what to do, once you know that it's mostly pretty easy, the game is definitely more of a social thing, I think most people playing would have a much better time playing with others and they're banking a lot of people creating their own stories.

EG has a good preview on it: https://www.eurogamer.net/articles/2018-03-20-sea-of-thieves-is-sandbox-gaming-at-its-purest Imo they should release their post-launch road-map now, I could see people reaching Pirate Legend fairly quickly.

I don't quite understand how to accept a quests, go on a quest, make sense of the map, etc. I guess part of it is learning how to play it.

It took me like an hour just figure out how make the ship move.

Yeah, a little messing around on the ship and you should get the hang of it eventually but I found this post which pretty much sums up the basics pretty good so I don't have to - https://www.resetera.com/threads/sea-of-thieves-ot-a-rare-treasure.30325/page-76#post-5802508

It's probably worth watching this video too: https://www.youtube.com/watch?v=OBJUG-Xrh_g

They definitely should have made a couple of tutorials, one for the basics of the trading factions and receiving quests, another for how to sail the ship.